1. The Field of the Invention
The present invention is related to the field of endodontistry. More particularly, the invention is related to the systems and methods for treating root canals.
2. The Relevant Technology
To preserve a tooth with a pulp that is diseased or is potentially diseased, it is generally necessary to remove the pulp material in the pulp canal from the tooth, to shape the root canal(s), to prevent or minimize the presence of bacteria through the use of irrigants and dressings, to clean the walls of the root canal(s), to eliminate the smear layer made during instrumentation of the root canal(s) to open the dentinal tubules. These steps are all done to prepare the root cavity for being filled or obturated with biocompatible materials, such as gutta percha, before the pulp cavity is sealed, thereby promoting the healing and functional recovery of the tooth. This procedure is referred to as root canal therapy.
Root canal preparation, which generally involves the pulp removal and cleaning of the root canal walls as well as shaping of the canal walls, is typically achieved by mechanical or hand instrumentation with files or bits that are configured to bore and/or cut. Mechanical instrumentation can be achieved through the use of endodontic handpieces that give instruments such as files a rotational motion, reciprocal motion, sonic movements or ultrasonic movements.
Before endodontic therapy is begun, a preoperative x-ray is prepared to assess the health and the pathological status of the tooth and to determine the approximate length of the the root canal in order to select an instrument for use in root canal with an appropriate working length. The x-ray yields an image, such as the schematic representations shown in FIGS. 1A and 1B, which generally show teeth 10 with sufficient clarity to view some of the properties of roots 12 and the root canals 14 located therein, particularly the location of the radiographic apex 17 just beyond the apical foramen 16. The distance between radiographic apex 17 and a fixed reference position on the occlusal surface of a tooth is used to determine the working length of the instrument. FIG. 1B, an enlarged view of root 12a shown in FIG. 1A, shows the relative position of the radiographic apex designated at line 17 with that of the endodontic apex and the anatomical apex designated respectively by lines 18 and 19.
Preoperative or intraoperative x-ray images of a tooth requiring endodontic treatment, such as the x-ray image depicted in FIG. 1A, are obtained by lingual placement of film packets as shown in FIG. 2 at 22 and by a x-ray film packet holder (not shown) and a long cone x-ray head (not shown) seated outside of the cheek. Although, x-ray images formed as shown in FIG. 2 from a buccal-lingual x-ray projection are generally useful for determining the length of the root canal and the working length for a file, such images provide only limited information regarding the overall anatomy of the root canal and can also be misleading as to the actual length of the root canal.
The information is limited because only one dimension of the overall anatomy of the pulp cavity can be viewed in vivo. Such images show only a linear aspect of the root canal but cannot show a tridimensional view of a tooth and its root canal(s). Although, it would be very helpful to view a tooth from a position between the teeth or from the interproximal space such a mesial-distal view cannot be clearly produced when the tooth is still positioned in a patient's mouth.
The difficulties presented to an endodontist in assessing the overall anatomy of teeth from just the x-ray images obtained from buccal-lingual x-ray projections can be clearly identified with reference to FIGS. 3-6. FIGS. 3A-6A are longitudinal cross-sectional schematic views of extracted teeth taken from the front or back of the respective tooth which corresponds with the images obtained from buccal-lingual x-ray projections. FIGS. 3B-6B depict longitudinal cross-sectional schematic views of the same extracted teeth shown in FIGS. 3A-6A from the mesial-distal or side view that cannot be obtained or seen while the teeth are still positioned in a patient's mouth.
FIGS. 3-4 illustrate the necessity for practioners to rely heavily on their experience and knowledge of typical anatomical structures to properly prepare a root canal. FIG. 3A depicts a lower premolar 30 from the buccal-lingual view of the tooth which shows root 32 and a root canal 34 therein that appears to be rather narrow and to have a relatively uniform perimeter along its length. FIG. 3B, however, shows that when seen from the mesial-distal view, the root canal is initially wide and then tapers significantly before reaching the apical foramen 36. The practioner may not be able to accurately assess the anatomical structure of the root anatomy when limited to knowledge derived from an x-ray corresponding to the image shown in FIG. 3A. Similarly, FIG. 4B, which depicts an upper premolar 40 with roots 42a and 42b and root canals 44a and 44b located therein, illustrates the need for practioners to rely merely on accumulated experience and knowledge of typical anatomical structures as the configuration of pulp chamber 48 may be difficult to accurately ascertain from only a x-ray photograph that corresponds with the image shown in FIG. 4A.
Additionally, practioners encounter anatomies with widely varying aberrations and intercommunications of root canals. FIG. 5A depicts a mandibular or lower incisor 50 from the buccal-lingual view of the tooth which shows root 52 and root canal 54. FIG. 5B depicts the same lower incisor 50 from the mesial-distal view of the tooth. The mesial-distal view shown in FIG. 5B clearly shows that root canal 54 branches and then merges to have a single foramen 56. This common root canal morphological variation shown in FIG. 5B may not be ascertainable to a practioner as the practioner can only obtain a preoperative or intraoperative x-ray image of lower incisor 50 which corresponds to FIG. 5A. Similarly, a root canal may branch without merging to yield multiple foramina as shown in FIGS. 6A-6B which depict a lower first molar 60. Again, the buccal-lingual view, as shown in FIG. 6A, provides inadequate information compared with the depiction taken from the mesial-distal view of mesial root 62b in FIG. 6B wherein branches 64a and 64b are shown which do not merge and accordingly have two foramina 66a and 66b.
In addition to the morphological variations in anatomy as discussed above, there are also substantially different perimetrical configurations of root canals. The shape of root canal perimeters varies not only between different types of teeth but also along the length of a single root canal of a tooth as is illustrated in FIGS. 7A-7B.
FIGS. 7A depicts a maxillary right first molar 70 with cutting lines which show the division of the tooth into transverse cross-sections for segmentation as shown in FIG. 7B. FIG. 7B displays roots, 72a, 72b and 72c, of molar 70 cut into four respective segments, 80-83, to clearly show the variations of root canals 74a, 74b and 74c. Also displayed in FIG. 7B are segments 84 and 85 which respectively contain the floor of the pulp chamber 78 and pulp chamber 78. Contrasting the perimeters of root canals 74a, 74b and 74c beginning in segment 84 as each root canal tapers to its respective apices 76a, 76b and 76c clearly shows that the perimeter anatomy varies along the length of each root canal.
As indicated above, root canals have a variety of perimetrical or circumferential anatomies depending on the type of tooth. Accordingly, the practioner must utilize instruments in root canals with diverse perimetrical anatomies that each also vary and transition in the configuration of their respective perimeters along their root canal lengths. FIG. 8 shows cross-sectional views of different teeth 90a-901 that have been extracted and then cut along a transverse cross-section of the tooth to show root canals 92a-921 as well as corresponding pulp chambers 94 and floors or cervical aspects 96. File instruments 98 are also shown inserted into root canals 92. From this view, which can only be seen in vitro, it is evident that a high degree of variation occurs in the perimetrical anatomy of the pulp cavity of teeth.
FIG. 9 shows the general division of root canal perimetrical anatomies into those that have primarily a tubular morphology and those that have primarily a laminar morphology. The tubular perimetrical anatomies include root canals such as those shown at 100, 101, and 102 which are respectively primarily oval, round and triangular. The laminar perimetrical anatomies include root canals with essentially slit-like configurations such as those shown at 103, 104, and 105 which are respectively primarily straight, semi-lunar shaped and figure eight shaped.
From the discussion above, it is apparent that when a practitioner views a preoperative or interoperative x-ray image of a tooth the practitioner can only guess about the actual anatomy of the pulp cavity and the root canal system. While the practitioner may be able to confirm that a root canal has been cleaned along the length of the pulp chamber from the coronal portion to the apex of the root, the length that has been contacted or abraded by the file may only be a portion of the root canal system.
However, without a correct understanding of the overall root canal anatomy due to the inability to see the root canal from the mesial-distal view or the perimetrical anatomy on different points along the length of the root canal, the practioner can never value the relationship between the instrument inserted in the root canal with the canal walls. Accordingly, as shown in FIGS 10, when a root canal 112a-c of a tooth 110a-c is cleaned by merely inserting a file instrument 114 into each tooth 112a-c and then rotating the instrument, significant portions are not cleaned. The inability to clean all surfaces of a root canal by merely inserting a file instrument is further illustrated in FIG. 8 wherein the position of file instrument 98 is shown in transverse cross-sectional views of root canals. FIG. 8 shows that boring from one position into the root canal will often miss large sections of the perimeter of the root canal, thereby leaving portions of diseased or necrotic pulp material undisturbed which can ultimately cause undue pain, lengthy healing times or even cause the procedure to fail. One of the reasons sodium hypochlorite is used is to compensate for the failure to adequately clean the entire perimeter.
The inability to fully identify the anatomy of the pulp cavity restricts the ability of the practitioner to confidently conclude that the procedure has been successful. However, many dentists are not overly concerned with completely cleaning the entire root canal since their failure rate is not at an unsatisfactory level.
To compensate for the inability to contact all root canal surfaces and the lack of knowledge of the actual anatomy of the root canal, conventional cleaning techniques involve sequential increases in the diameter of instruments inserted into the root canal. The primary conventional systems and methods for removing pulp material from the root canal of a tooth are the step-back technique and the crown-down technique. The step-back technique involves cleaning the root canal from the apex to the crown while the crown-down technique involves cleaning the root canal from the crown down to the apex. Each has its own unique benefits and disadvantages.
The step-back technique involves the use of a set of file instruments which are sequentially inserted into a root canal after the root canal has been exposed by removing the roof of the pulp chamber as shown in FIG. 11A and FIG. 11B with an instrument 120 with bur 122. After the overhanging portions of enamel 152 and dentin 154 have been removed to provide access into the pulp chamber, pulp material 160 can be removed. FIG. 12 depicts a set of step-back file instruments with each file instrument 130 comprising a handle 132 connected to a file 134 or a shaft with tines or an abrading portion. Each file has a tip 136 opposite atop end 138 where file 134 joins handle 132. As viewed in FIG. 12 from left to right, the diameter at top end 138 of each file increases progressively from the smallest to the largest such that the diameter of 138a is less than the diameter of 138b. The diameter of each successive file at tip end 136 is also successively larger. Accordingly, the taper of each file remains essentially the same even though each file is progressively larger that the preceding file.
In the step-back technique, the apical portion of the tooth is prepared first and then the canal is flared from apex to crown. The process essentially involves inserting a series of progressively larger files to the apex of the root canal and rotating each file and/or moving the file up and down in a longitudinal motion until a file can be entered that is considered a standard size for completing the process or that meets some resistance to rotation. The rest of the canal is then flared by sequentially using each file in the set as shown in FIG. 12 with each file being larger than the preceding file and by alternately advancing and then withdrawing each instrument.
FIG. 13A depicts molar 150 being prepared by the step-back technique after the enamel 152 and dentin 154 have been removed that overhang pulp chamber 156 and after the first step of the step-back technique has been achieved by inserting a file into pulp chamber 156 and into root canal 158a to remove material 160 in the lower portion of the canal above the apex or apical end 162a. After the portion above apex 162a is cleaned, each file shown in FIG. 12 is sequentially inserted down to apical end 162a of root canal 158a beginning as shown in FIG. 13A with file instrument 130a. As a result of this technique, the diameter of the area being contacted at the apical portion is increasingly larger.
FIG. 13B is a cross-sectional view taken along cutting line 13B--13B in step-back technique. Insertion of the files of the other file instruments 130b and 130c will further clean material 160 as the diameter of each file is increasingly larger, however, the files are also increasingly rigid. As the rigidity increases, the flexibility of the files decreases and as result it becomes increasingly difficult for the files to adjust to the contours of the surfaces of the root canal to clean all of the surfaces of the root canal and increases the likelihood that the files will remove too much of the surrounding dentin 154.
The views depicted in FIGS. 13A and 13B depict the problem previously discussed with regard to the difficulty in assessing the actual root canal anatomy in vivo. When viewed in FIG. 13A, it appears that the root canal has been cleaned, however, FIG. 13B shows that a significant portion of material 160 remains. Accordingly, when the root canal is viewed in an x-ray photograph which is the same view shown in FIG. 13A, a practitioner may mistakenly believe that the tooth has been adequately cleaned. This mistaken belief may be further incorrectly relied on as the root canal is widened by the insertion of the larger files and the large files cannot be used to properly follow the contours of the root canal to fully clean the root canal. Accordingly, there is some possibility for failure of the root canal therapy.
Additionally, since each file is more rigid than the preceding file, which limits the ability to safely move the file within the canal is limited. Further, the increasing rigidity results in decreased ability to negotiate the curves in the canal and to clean all of the surfaces or walls of the canal. A significant problem that can result from inserting increasingly rigid files and also from initially inserting a file all the way down to the apex is apical perforation. As shown in FIG. 14A, after tooth 170 has been prepared by removal of portions of the enamel 172 and dentin 174, file 132 has been inserted into root canal 176 and perforated apex 178. Perforating the apex can also result from an error in estimating the length of a root canal, by failure of a stop such as stop 140 to remain at a predetermined position or by failure to observe the hatch markings on the file which can be used instead of a stop to designate the length.
The apex can be perforated by extrusion of the infected material 180 through the apex due to the force exerted by the file on the material as the file is pushed downward to reach the apex. The potential for extruding infected material through the apical foramen of a necrotic tooth by initially inserting a file instrument all the way down to the apex is a particular disadvantage of the step-back technique. More particularly, it is a disadvantage that the procedure has identical steps for working in either necrotic or vital root canals. In addition to exposing the tissue surrounding the tooth to the infected material, apical perforations may allow irrigants and filling or obturating material to flow out of the apex. Such apical perforations, as well as wall perforation, may delay tooth healing and may compromise the outcome of the therpy.
Perforations can also occur due to a failure to maintain a proper working length of the instrument during the procedure. As the canal is widened, curvatures are straightened which decreases the length needed for the instrument to work. Accordingly, the rubber stop 140 must be adjusted. To properly determine the appropriate working length, many radiographs are necessary throughout the operation as the canal is modified. The time required to obtain the x-ray photographs or images and to adjust the working length of the instruments results in a lengthy process. The step-back technique is also time intensive as a large number of instruments are required to complete the root canal therapy.
As shown in FIG. 14B another problem is the formation of ledges such as ledge 182. Ledges can occur when a practitioner attempts to insert a file such as file 134 to the apex and the file is too inflexible to properly curve with the root canal or move around a protrusion. When a file is too inflexible to flex as needed and prematurely comes to a stop, the downward pressure exerted on the file causes the file to dig into the side of the root canal and form a ledge. Such ledges are difficult to bypass and if the ledge occurs very close to the apex, the ledge may give the practitioner the mistaken impression that the apex has been reached.
The crown-down technique was developed partially to decrease the amount of instrumentation required to clean a root canal by the step-back technique. However, the crown-down technique does not avoid the problems set forth above in relation to the potential for perforation and ledging.
The crown-down technique generally involves the use of a set of file instruments wherein each file in the set of file instruments has a different diameter at the top of the file where the file joins the handle. The diameter at the top of each file is progressively larger than the preceding file. As a result of this configuration, the taper of each file is larger than the preceding file in the set. By using such files, the area being abraded, particularly in the anatomical coronal portion, is abraded with files of increasingly larger diameters.
Based on the greater flexibility of files formed from nickel/titanium compared with files formed from steel, proponents of nickel/titanium files have asserted that such nickel/titanium files are more likely to follow root canal curvatures and to stay in the center of the root canal, thereby decreasing the likelihood of ledging or perforating the root canal walls. As set forth hereinbelow in greater detail, each material has its own unique advantages and disadvantages.
The ability of a nickel/titanium file to stay in the center is not necessarily desirable. By remaining in the center, the file instrument works contemporaneously and indiscriminately on all walls within reach of the file. Since root canal walls do not have equal thicknesses in all direction and at all different points along a root canal, some walls can be overthinned or perforated. Additionally, nickel/titanium file instruments can be too flexible to adequately clean the root canal as the file may bend and be deformed when it encounters a hard substance. Since the nickel/titanium files are flexible, they tend to follow the path of least resistance and cannot be used to aggressively clean the portions that are difficult to reach. Accordingly, when a nickel/titanium file is used to clean a non-cylindrically shaped root canal, the file moves only at the center of the canal and/or the area of least resistance and fails to remove all of the necrotic tissue.
FIGS. 15A, 15B, 15C, 15D and 15E depict transverse cross-sections of a tooth 190 that has been cleaned in a manner that has resulted in either overthinning of root canal walls, perforation of a root canal wall or excessively weakening of a tooth. These problems result primarily from the use of files with increasingly larger tapers and increasing rigidity in accordance with the crown-down technique which prevents the files from being laterally moved to enable the file to clean the entire perimeter of the root canal. The cross-sections shown in FIGS. 15A-E may be considered independently from each other as being cross-sections from a different teeth or from a single tooth such that FIG. 15A shows two roots 192a and 192b of a tooth 190 while FIGS. 15B-15E show root canal 194a as the root canal tapers to the apex.
FIG. 15A depicts the overthinning that can occur to the function walls of root canals 194a and 194b as a result from the indiscriminate thinning of root canal walls by maintaining a file instrument in a central location. Such overthinning and potential furcal perforation can have devastating results. The inability to adequately direct a file used in accordance with the crown-down technique based on the practioner's knowledge of the relative thicknesses of the portions of canal walls is a significant disadvantage of the technique.
In FIG. 15B, a lateral perforation has occurred as a hole has been formed through dentin 198 and cementum 197 during the cleaning of root canal 194a. The lateral perforation resulting from the formation of borehole 196a may be obscured from the x-ray. The practitioner may then mistakenly conclude that the root canal has been successfully cleaned without realizing that there is a perforation.
In FIG. 15C, root canal 194a has been overly thinned as borehole 196a extended through dentin 198 and into the cementum 197 during the cleaning of root canal 194a. As in FIG. 15B, the excessive thinning resulting from the formation of borehole 196a may be obscured from the x-ray view due to concavities or curvatures in the root canal. As a result, the practitioner may not realize conclude that the root canal has been successfully cleaned without realizing that the borehole extends into the cementum and may therefore mistakenly conclude that the root canal treatment has been successful. Infective bacteria that remained in the root canal, perhaps in the portions that were not contacted with the files, as well as toxins produced by the bacteria may then permeate through the cementum and cause infection or other complications.
Root canal therapy resulting in the configuration shown in FIG. 15D may be successful even though only a portion of root canal 194a has been cleaned as evidenced by borehole 196a. It would, however, be preferable to be able to remove and clean essentially all pulp material by cleaning the entire perimeter. Although, it would be preferred to clean the root canal without missing significant portions, the configuration shown in FIG. 15D is the standard result of the crown-down technique. As with the step-back technique shown in progress in FIGS. 13A and 13B, the x-ray view of tooth 190 would give the impression that the root canal had been cleaned. Additionally, the use of a set of files with increasing tapers would further contribute to a potentially incorrect conclusion that cleaning by such a conventional process had resulted in removing all material from root canal 194a.
As in the configuration shown in FIG. 15D, the configuration shown in FIG. 15E may also result in successful root canal therapy. Although, borehole 196a does not extend through dentin 198 and into the cementum 197, the borehole 196a is significantly larger than root canal 194a was as shown by the phatom line. The excessive thinning may resultingly significantly weaken tooth 190.
The configuration of the large borehole 196a as shown best in FIGS. 15B, 15C, 15D and 15E results primarily due to the shape and properties of the files. The use of files with increasingly larger tapers limits the range of motion of the files. Due to the use of files with successively larger tapers which therefore are increasingly rigid, each file is primarily limited to being rotated without substantial lateral movement such that the tip of each file acts as a rotation point and remains in essentially the same location as the file is rotated. Each successive file can move less laterally and makes a bigger borehole than the preceding file. Accordingly, the files cannot clean a root canal without significantly altering the original anatomy by leaving a footprint or borehole corresponding to the configuration of the instruments used. More specifically, the result is a footprint or borehole with a perimeter that corresponds to the perimeter of the biggest file that extends well beyond the original anatomy of the root canal and yet in most instances does not adequately clean significant portions of the root canal.
The configuration of borehole 196a, which substantially deviates from the original anatomy of the root canal 194a, is due also to the flexibility of the files used in the crown-down technique which are typically formed from nickel/titanium. The flexibility of the files prevents the files from being successfully urged against the perimeter or against the various surface features of the root canal. The flexibility of the files also increases the tendency of the files to remain in the center or at the location where less resistance to movement is encountered.
There are also other disadvantages to the use of nickel/titanium files. Nickel embodied in the alloy may potentially result in an allergic reaction. Nickel/titanium files are brittler and softer than stainless steel. Accordingly, nickel/titanium files may break more easily and suddenly than steel. When a nickel/titanium file instrument is used with a large file diameter the flexibility decreases to the point of being as rigid as stainless steel and yet it can break more easily. Additionally, nickel/titanium files costs about four times as much as steel files and yet nickel/titanium files generally wear out faster than steel files. Nickel/titanium files wear out so quickly that some manufacturers mark their products as being intended for single use only.
Although, the crown-down technique typically enables a practitioner to more efficiently clean a root canal than the step-back technique, they both require the practitioner to utilize many different instruments, The need to frequently change the cleaning instrument results in significant time requirements for cleaning a root canal. However, careful instrumentation in accordance with either tedious time consuming method does not avoid the problems set forth above in relation to apical perforation, wall perforation, overthinning or failure to clean all of the wall surfaces.
Based on the foregoing, methods and systems are needed in the endodontic arts which enable a dental practitioner to remove and clean essentially all pulp material in a root canal requiring root canal therapy.
It would also be an advancement in the endodontic arts to provide methods and systems that enable a practitioner to remove and clean pulp material in a root canal in a safer a manner than conventional techniques and which does not substantially alter the anatomy of the root canal.
Additionally, it would be an advancement in the endodontic arts to provide methods and systems that enable a practitioner to remove and clean pulp material in a root canal in a manner that is at least as efficient as conventional techniques and is less likely to result in failure due to overly thinning the root canal, perforations or due to infected material being pushed beyond the root from the coronal aspects of canals.